Conventionally, as this type of floating seal, a floating seal having a configuration disclosed in, for example, Patent Document 1 has been proposed. In the floating seal with this conventional configuration, a fixed floating ring formed of metal material is elastically supported by an inner circumferential surface of a fixed housing through an elastic ring formed of nitrile rubber or the like. A rotating floating ring formed of the same metal material as that of the fixed floating ring is elastically supported by an inner circumferential surface of a rotating housing through an elastic ring formed of the same elastic material as that of the other elastic ring.
The floating rings are held together in a sealing state by the elasticity of the elastic rings. When the rotating housing is rotated, the floating rings slide with respect to each other. Since the floating rings are maintained in a tight contact state, oil is prevented from leaking from inside the housings.
If the contact surface of any one of the elastic rings and that of the associated one of the floating rings of the floating seal slide with respect to each other, the elastic ring wears prematurely and thus becomes damaged. This degrades the performance of the elastic ring to apply elasticity to the floating ring, thus lowering the sealing performance of the floating ring. To avoid this problem, as illustrated in FIG. 8, for example, a rough surface 43 is formed on the contact surface of a floating ring 42 with respect to an elastic ring 41 to increase the friction coefficient. This prevents the elastic ring and the floating ring from sliding with respect to each other.    Patent Document 1: Japanese Laid-Open Utility Model Publication No. 62-25374